The Friedel-Crafts alkylation of benzene has been widely employed as a method of producing synthetic lubricant base oils. The dialkyl benzenes, R.sub.1 --C.sub.6 H.sub.4 R.sub.2, wherein R.sub.1 and R.sub.2 are alkyl groups containing from 8 to 18 and more usually from 10 to 15 carbon atoms and C.sub.6 H.sub.4 represents the benzene nucleus, have received the most attention, inasmuch as they are produced as by-products during the manufacture of sodium alkyl benzene sulfonate laundry detergents. Originally, the alkyl substituents were derived from propylene tetramers and similar highly branched olefins; and, as a consequence of this branching, the dialkyl benzenes, while possessing good thermal stability, had extremely poor viscosity-temperature characteristics, as illustrated by viscosity indexes generally below zero. More recently, linear alpha-olefins and linear monochlorinated paraffins have replaced tetrapropylene in the alkylation, and many of the resulting dialkyl benzenes have good viscosity indexes as well as good thermal stability and low temperature properties. Representative properties of dialkyl benzene base oils are: viscosities at 210.degree.F. of from 4 to 6 centistokes; viscosity indexes of around 100; pour points below -40.degree.; flash points have above 400.degree. F. Among the many references to the preparation and use of dialtyl benzenes are Bray et al, U.S. Pat. Nos. 3,478,113; Bray et al, 3,544,472; Pappas et al, 3,173,965; Becraft et al, 3,288,716; and Feighner et al, 3,662,012. The many applications found for these products include power transmission oils, hydraulic fluids, automobile crankcase oils, especially for automobiles operating in exceptionally cold climates, and gas turbine lubricants, where high temperature stability is important.
Monoalkyl benzenes, on the other hand, are not as generally useful in such applications as their dialkyl benzene counterparts. One of the main problems is their poor low temperature properties. For example, Pappas et al, in U.S. Pat. No. 3,173,965 describe a di--C.sub.10 --C.sub.15 alkyl benzene with a pour point of below 75.degree. F. On the other hand, the same workers prepared two mono-C.sub.18 -alkyl benzene and 1-octadecone, and found pour points of +23.degree. F. and -7.degree. F. respectively, even though the two monoalkyl benzenes had lower molecular weights, lower viscosities at 210.degree. F. and higher viscosity indexes than the di--C.sub.10 --C.sub.15 alkyl benzene above. Lower molecular weight monoalkyl benzenes such as tridecyl benzene have better low temperature properties but their relatively low flash points (300.degree. - 350.degree. F.) and viscosities (from 1.5 to 3 centistokes at 210.degree. F.) make them unsuitable for high temperature applications for which the dialkyl benzenes can be used.